Fluorescent particles are useful in various applications. For instance, fluorophores are useful as fluorescent probes, such as labels or tags, e.g., in many biochemical fields, such as drug and gene research, cell/microorganism imaging, disease diagnosis, analyte detection, and the like. Conventional fluorophores include organic dyes, green fluorescent proteins (GFP) and their mutants, water-soluble conjugated fluorescent polymers, quantum dots (QD), and the like.
However, conventional fluorophores have some drawbacks. For example, the manufacturing processes of multi-color organic dyes and GFPs are complicated. Further, the performance of these fluorophores often depends on the surrounding environment, thus rendering them unstable and unreliable, even unsuitable in certain environments. In addition, GFPs have low luminescence, especially in the blue and red spectral regions. Water-soluble conjugated fluorescent polymers, like organic dyes and GFPS, are sensitive to conditions of the external environment, such as pH values or ionic strength of the surrounding solution. Another problem is that many fluorophores, including many fluorescent polymers, cannot be dissolved in water to form a stable and homogenous solution, which significantly limits their application, as aqueous environments are the most common environments in nature.
A known technique of solubilizing hydrophobic fluorescent nanocrystals in aqueous solutions is to wrap nanocrystals with cross-linked amphiphilic polymers to form water-soluble QDs. However, this approach has the disadvantage of requiring complicated preparation steps, as the amphiphilic polymers not only have to form shells around the nanocrystal cores, the amphiphilic polymers also have to be cross-linked after they form the shells. Further, QDs have other shortcomings. The formation process of QDs typically requires elevated temperatures and it is difficult to produce QDs with both high luminescence and narrow emission spectra. In addition, QDs have limited application in certain fields, such as single-molecule imaging in live cells, which typically involves photobleaching or fluorescence blinking. As QDs have high photo-stability, they are difficult to photobleach. As QDs have long blinking intervals, they are unsuitable for use in fluorescence blinking procedures.